1. Technical Field
The present invention relates to a rotor for an electric motor, which comprises a plurality of annular rotor discs, stacked into an axial disc assembly, for securing a plurality of permanent bar magnets, of substantially rectangular cross-sectional shape, distributed around the circumference of the rotor, wherein the rotor discs have pockets of substantially corresponding cross-sectional shape for accommodating and securing the permanent bar magnets in such a way that adjoining bars form an angle to one another and to a radius of the rotor, and that at least a portion of one end edge of each bar is exposed to the outer periphery of the disc assembly.
The invention also relates to an annular rotor disc for, in an axially stacked disc assembly of a plurality of similar rotor discs, forming a rotor for an electric motor, and to an electric motor having such a rotor.
2. Related Art
In rotors for certain types of electric motors (PM motors), annular, so-called rotor discs are used, which are stacked axially to overlap one another and which are configured to support axially running permanent magnets distributed around the circumference. Usually, these permanent magnets are surface-mounted on the periphery of the rotor by gluing or they are mounted buried in closed pockets in the disc elements of the rotor. The pockets in the discs can also be made open towards the outer periphery of the rotor in order that the permanent magnets shall be exposed to the stator with a small air gap between the stator and the rotor, which gives a reduced magnetic leakage and increased magnetic flux.
Through JP 2000-116042 A, a PM motor is previously known, the rotor of which is constructed of a large number of axially overlapping rotor discs having tangential and, at one end at least, open slots for the insertion and securement of permanent magnets, the open slots opening out towards the periphery of the rotor in order to increase the magnetic flux and reduce magnetic leakage. For secure fixing of the permanent magnets in the rotor, two different discs and possibly gluing are required.
WO 00/62399 shows a rotor for an electric motor, in which various types of rotor discs are required to secure permanent magnets placed in a V-shape in such a way that one end of the magnets is held exposed towards the outer periphery of the rotor, which adds to the difficulty and cost of assembly.
DE 202 01 831 U1 describes a rotor disc for PM motors, in which tangentially orientated magnets are held clamped on the periphery with the aid of resilient plates, which, without glue, allow secure surface-mounting of the magnets with a single type of rotor disc, the magnets being able to be situated close to a small air gap between rotor and stator. However, there is a relatively large air gap to the rotor disc radially within the magnets and a small contact surface therebetween, which adversely affects the magnetic flux in the rotor itself. The tangential placement of the magnets also means that the number of magnets is severely limited, as is the total magnetic flux.